Connect to the oscillator of the transmitter - good girl! You need to enable pre emphasis in this case. Connect to the discriminator of the receiver - good boy! You need to enable de emphasis in this case.pull/1/head
Andreas Eversberg
7 years ago
parent
5062628e52
commit
4356c93afa
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/* Pre-Emphasis and De-Emphasis implementation
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* |
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* (C) 2016 by Andreas Eversberg <jolly@eversberg.eu> |
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* All Rights Reserved |
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* |
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* This program is free software: you can redistribute it and/or modify |
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* it under the terms of the GNU General Public License as published by |
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* the Free Software Foundation, either version 3 of the License, or |
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* (at your option) any later version. |
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* |
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* This program is distributed in the hope that it will be useful, |
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* but WITHOUT ANY WARRANTY; without even the implied warranty of |
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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* GNU General Public License for more details. |
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* |
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* You should have received a copy of the GNU General Public License |
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/ |
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#include <stdio.h> |
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#include <stdint.h> |
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#include <string.h> |
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#include <math.h> |
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#include "emphasis.h" |
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#include "debug.h" |
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int init_emphasis(emphasis_t *state, int samplerate) |
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{ |
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double factor; |
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memset(state, 0, sizeof(*state)); |
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if (samplerate < 24000) { |
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PDEBUG(DDSP, DEBUG_ERROR, "Sample rate must be at least 24000 Hz!\n"); |
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return -1; |
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} |
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factor = 0.95; |
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state->p.factor = factor; |
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state->p.amp = samplerate / 48000.0 * 4.0; /* mysterious 48000 */ |
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state->d.factor = factor; |
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state->d.amp = 1.0 / (samplerate / 48000.0 * 4.0); /* mysterious 48000 */ |
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return 0; |
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} |
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void pre_emphasis(emphasis_t *state, int16_t *samples, int num) |
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{ |
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int32_t sample; |
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double old_value, new_value, last_value, factor, amp; |
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int i; |
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last_value = state->p.last_value; |
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factor = state->p.factor; |
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amp = state->p.amp; |
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for (i = 0; i < num; i++) { |
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old_value = (double)(*samples) / 32768.0; |
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new_value = old_value - factor * last_value; |
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last_value = old_value; |
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sample = (int)(amp * new_value * 32768.0); |
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if (sample > 32767) |
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sample = 32767; |
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else if (sample < -32768) |
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sample = -32768; |
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*samples++ = sample; |
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} |
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state->p.last_value = last_value; |
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} |
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void de_emphasis(emphasis_t *state, int16_t *samples, int num) |
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{ |
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int32_t sample; |
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double old_value, new_value, last_value, factor, amp; |
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int i; |
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last_value = state->d.last_value; |
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factor = state->d.factor; |
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amp = state->d.amp; |
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for (i = 0; i < num; i++) { |
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old_value = (double)(*samples) / 32768.0; |
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new_value = old_value + factor * last_value; |
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last_value = new_value; |
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sample = (int)(amp * new_value * 32768.0); |
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if (sample > 32767) |
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sample = 32767; |
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else if (sample < -32768) |
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sample = -32768; |
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*samples++ = sample; |
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} |
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state->d.last_value = last_value; |
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} |
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@ -0,0 +1,17 @@ |
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typedef struct emphasis { |
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struct { |
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double last_value; |
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double factor; |
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double amp; |
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} p; |
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struct { |
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double last_value; |
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double factor; |
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double amp; |
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} d; |
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} emphasis_t; |
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int init_emphasis(emphasis_t *state, int samplerate); |
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void pre_emphasis(emphasis_t *state, int16_t *samples, int num); |
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void de_emphasis(emphasis_t *state, int16_t *samples, int num); |
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@ -0,0 +1,75 @@ |
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#include <stdio.h> |
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#include <stdint.h> |
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#include <math.h> |
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#include <string.h> |
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#include "../common/emphasis.h" |
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#define level2db(level) (20 * log10(level)) |
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#define db2level(db) pow(10, (double)db / 20.0) |
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#define SAMPLERATE 48000 |
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#define DEVIATION 8000.0 |
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static void check_level(int16_t *samples, const char *desc) |
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{ |
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int i; |
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int last = 0, envelope = 0; |
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int up = 0; |
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int freq; |
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for (i = 0; i < SAMPLERATE; i++) { |
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if (last < samples[i]) { |
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up = 1; |
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} else if (last > samples[i]) { |
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if (up) { |
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envelope = last; |
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} |
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up = 0; |
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} |
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if ((i % (SAMPLERATE/40)) == 0) { |
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freq = 500 + 500 * (i / (SAMPLERATE / 8)); |
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printf("%s: f = %d envelop = %.4f\n", desc, freq, level2db((double)envelope / DEVIATION)); |
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} |
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last = samples[i]; |
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} |
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} |
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static void gen_samples(int16_t *samples) |
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{ |
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int i; |
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double value; |
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int freq; |
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for (i = 0; i < SAMPLERATE; i++) { |
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freq = 500 + 500 * (i / (SAMPLERATE / 8)); |
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value = sin(2.0 * M_PI * (double)freq / (double)SAMPLERATE * (double)i); |
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samples[i] = value * DEVIATION; |
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} |
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} |
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int main(void) |
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{ |
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emphasis_t estate; |
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int16_t samples[SAMPLERATE]; |
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/* generate sweep 0..4khz */ |
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gen_samples(samples); |
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init_emphasis(&estate, SAMPLERATE); |
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// check_level(samples, "unchanged");
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pre_emphasis(&estate, samples, SAMPLERATE); |
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check_level(samples, "pre-emphasis"); |
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/* generate sweep 0..4khz */ |
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gen_samples(samples); |
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de_emphasis(&estate, samples, SAMPLERATE); |
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check_level(samples, "de-emphasis"); |
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return 0; |
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} |
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